Design and Implementation of Quart-Torus Waveguide Filters for Layout Optimization Using Additive Manufacturing Techniques

In this contribution, a novel quart-torus cavity for the design of waveguide filters is presented. A filter breadboard based on this kind of cavity is designed at $Ku$ -band, and then fabricated using additive manufacturing (AM) techniques. The objective is to optimize the footprint distribution of cavity filter structures without compromising their electrical performance. The proposed resonator is built by applying a circular revolution process to a 2-D surface generator. The presented study is performed for circular and elliptical cross-sectional quart-torus cavities. The resonances found in the proposed cavities show similar theoretical unloaded- $Q$ factors ( $Q_{U}$ ) to their equivalent circular waveguide cavities (around $Q_{U}=5000$ ), while exhibiting interesting advantages in terms of physical layout disposition, due to the bending applied. To demonstrate the feasibility of the proposed idea, a tenth-order in-line bandpass filter is designed with elliptical quart-torus (EQT) cavities. Due to the geometrical complexity, a prototype is manufactured using a selective laser melting (SLM) technique, and its measured response has shown very good agreement with respect to the full-wave simulations from the ideal designs. Measured results show a fractional bandwidth (FBW) of 5.3%, with return losses (RLs) better than 20 dB, and unloaded quality factor ( $Q_{U}$ ) above 700. The footprint optimization and flexibility offered by the new concept can make these AM filters a very attractive option for the microwave industry.